Most vehicles rely on a liquid cooling system to regulate engine temperature. A mixture of water and antifreeze flows through channels and absorbs the heat produced by the engine. The heated liquid then travels to the radiator, which transfers the heat out of the coolant and into the air. If you think your relay is failing, be sure to read common fan relay failures here .
This system works best when the vehicle is moving as it forces more air through the grill and into the radiator, increasing its efficiency. But what happens if the car is idling and is stopped? That’s where the cooling fan comes into play. Helps move air through the radiator even when the vehicle is not moving.
What does a cooling fan relay do?
The cooling fan relay is an electromagnetic switch that controls the power supply to the engine cooling fans . It ensures that power-hungry devices only work when needed, typically when the vehicle is stationary.
When engine temperatures approach unsafe levels, the vehicle’s computer or temperature switch turns on the cooling fan relay. The activated relay completes a circuit, allowing an electrical current to flow through it and to the cooling fans.
Most modern vehicles have relay controlled electric fans, which are vital in keeping the engine cool. The relay controls the engine cooling fans as well as the air conditioning condenser fan. It also saves electricity.
Since excessive heat will damage vehicle parts over time, a bad relay should be replaced as soon as possible .
Common Electric Fan Relay Symptoms and Faults
The relay is a critical part of the refrigeration system. When it malfunctions or breaks, it affects the fan. The problem extends to the rest of the cooling system, to the engine and to the entire vehicle.
Fortunately, there are signs that warn the driver of a problematic relay. Keep an eye out for the following common electric fan relay symptoms and failures.
1- The engine heats up or overheats
Does the engine get hotter than normal? Does it overheat faster and without warning? The problem may come from a malfunctioning cooling fan relay. Also, heat problems often make themselves felt when the vehicle is at rest .
However, a faulty cooling fan relay isn’t the only culprit for excessively high engine temperatures. Many other problems can cause the engine to run hot or overheat.
2- The cooling fans do not work
Instead of unusually high engine temperature, the driver may notice that the cooling fans have stopped working. A faulty or broken relay cannot supply power to the cooling fans. In turn, the fans without power will not work, leaving the radiator to fend for itself.
Without the helpful airflow from the fans, the radiator can’t remove as much heat as it usually does. It sends the still-warm coolant back into the engine, causing temperatures to rise as the coolant fails to do its job of cooling the engine.
3- Cooling fans keep running
Conversely, the cooling fans can continue to run even when the engine is off. This strange behavior indicates a different problem in the relay that controls the fans.
A short in the relay can permanently lock the armature in its open position. As a result, power will continue to flow to the electric motor, keeping the fans running continuously.
The vehicle’s battery provides power to electrical devices such as cooling fans. It only stores an amount of charge. If the fans are running all the time, they will drain the battery faster than normal.
4- Warning lights
If the cooling fan relay has failed, warnings may appear on the dash such as the check engine light and temperature warning light. This is one of the common electric fan relay failures that you can easily detect.
5- Air conditioning malfunction
A faulty cooling fan relay can also negatively affect air conditioning (A/C) performance. The reason, on most vehicles, is that the cooling fan doubles as a condenser fan. When the air conditioner is turned on, the fan moves air through the A/C condenser , thus removing heat from the refrigerant vapor inside.
Possible Causes of a Bad Cooling Fan Relay
Cooling fan relays can stop working for a number of reasons. The most common causes of relay failures are:
How to tell if the cooling fan relay is bad?
There are several ways to tell if a bad cooling fan relay is to blame for an overheated engine. The easiest method is to start the engine and then turn on the air conditioning. If the fan does not turn on, the cooling fan relay may be bad.
Because? Because as mentioned above, most cars use the same fan for the radiator and the air conditioning condenser. However, there are some models that use a second unit dedicated to the condenser. In this case, the condenser fan and the radiator fan may or may not share the same relay.
If the cooling fan is not working, you can check if the relay is the culprit by replacing it with another one. Many car relays are of a similar design, so you can just take one from a different, non-critical system and insert it in place of the cooling fan relay.
You’ll know the cooling system relay is faulty if the fan works with the replacement relay. You can also measure the resistance of the relay coil. The resistance of a normal relay will have a value between 40 and 80 ohms. Higher resistance levels warn that the coil has started to fail , while lower readings mean that the relay has gone bad.
Another DIY test is to shake the cooling fan relay and listen for any noise. A broken armature will rattle around the relay.
Cooling Fan Relay Types
There are various types of cooling fan relays. Their main difference lies in the armor they use to complete an electrical circuit.
1- Relay normally open
The most common type of relay uses an open armature. When the relay coil is energized, the armature closes. The completed circuit allows current to flow to the fan motor.
2- Relay normally closed
Unlike the normally open relay, this type uses a closed armature. Energizing the relay coil opens the armature and completes the circuit.
3- Double relay
This type of relay uses two circuits, one of which employs an open armature while the other has a closed armature. Thanks to the use of both armatures, a double relay can conduct an electrical current in both the open and closed positions .